Currently, in terms of driving for a light emitting unit, the driving for the light emitting unit (e.g., LED 1˜LED N) is generally realized by using resistors connected with several light emitting units in series in low end application, as shown in FIG. 1. Such scheme causes an output current to vary with variation of an input voltage, resulting in unstablility or flicker of LEDs' brightness. In high end application, a pulse width modulation dimming integrated circuit (PWM IC), for example, a buck circuit and a boost circuit, is usually adopted. Such scheme has a high cost and circuit configuration is complicated.
Further, in terms of soft switching on/off of the light emitting unit, thermal inertia is utilized to realize soft switching on/off in some applications using an incandescent lamp in early times. At present, in order to realize a soft switching on/off function, a programmable microcontroller is often adopted to regulate a PWM control signal, and such scheme has a high cost.
Moreover, in terms of dimming of the light emitting unit, a controllable PWM IC is adopted widely, and an additional logical signal is used to perform dimming. Since an additional control signal is required, system design is complicated while the cost is high.